/serr/ , n.
1. a respectful or formal term of address used to a man: No, sir.
2. ( cap. ) the distinctive title of a knight or baronet: Sir Walter Scott.
3. ( cap. ) a title of respect for some notable personage of ancient times: Sir Pandarus of Troy.
4. a lord or gentleman: noble sirs and ladies.
5. an ironic or humorous title of respect: sir critic.
6. Archaic. a title of respect used before a noun to designate profession, rank, etc.: sir priest; sir clerk.
[ 1250-1300; ME; unstressed var. of SIRE ]